Phytophthora Root and Stem Rot

Guy Padgett  |  5/2/2013 9:32:37 PM

Phytophthora root and stem rot.

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Phytophthora Root and Stem Rot (Phytophthora sojae)
Gerard T. Berggren

LSU AgCenter (retired)

This soil borne disease is largely confined to poorly drained clay soils, but may occur on other soils. Severe plant losses and yield reductions are common in susceptible cultivars. The fungus survives on crop debris in the soil, but can also survive in the soil for long periods without the presence of soybeans. Disease outbreaks are associated with periods of high soil moisture and rainfall. Infection and damage occur at any stage of growth.

Symptoms include stand reduction caused by seed rots or preemergence damping off. Postemergent symptoms include water soaked lesions on the stem and roots, yellowing of leaves, wilting, and seedling death. Older plants are killed more slowly. Leaves on older plants become chlorotic between the veins followed by a general wilting and death. The withered leaves generally remain attached. Lower stems have dark brown lesions that often extend beyond the first trifoliolate leaves.

The disease is best managed by planting resistant cultivars. Numerous races of the pathogen have been identified, but cultivars with resistance to all races are available. Low, poorly drained fields with a history of Phytophthora should be avoided.

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